I set 108 eggs. Culled about 12 at day 7 for clears or blood rings. Culled again at day 11, 13 this time. One last cull at 14, down to 67 now, not great but still at +50%. I now have about 18 that are hatching rest dead. My question is what would cause so many late deaths? Almost all are well formed. The eggs are clean, I didnt wash them. Not my first hatch with this incubator, I have done well with it before. I suspect I may not have adequate ventalation, there is a 1.25" square hole on back and a fan on the inside. Thoughts? No odor from the dead, at all.